1. Field of the Invention
The present invention generally relates to a method for fabricating devices on semiconductor substrates. More specifically, the invention relates to a method for removing conductive residue.
2. Description of the Related Art
Microelectronic devices are generally fabricated on a semiconductor substrate as integrated circuits wherein various conductive layers are interconnected to one another to facilitate propagation of electronic signals within the device. An example of such a device is a storage element in magneto-resistive random access memories (MRAM) that facilitate storage of digital information in a form of the direction of magnetization of a magnetic material within the MRAM.
A memory cell in an MRAM device generally is a multi-layered structure comprising a pair of magnetic layers separated by a tunnel layer. More specifically, the MRAM device comprises a free (or top) magnetic layer that may change a direction of magnetization and a bottom magnetic layer that has a fixed direction of magnetization. The magnetic layers are separated by the tunnel layer formed of a non-magnetic dielectric material, such as aluminum oxide (Al2O3) and the like. The top and bottom magnetic layers may each comprise a plurality of sub-layers of magnetic materials, e.g., permalloy (NiFe), cobalt iron (CoFe), and the like. The top and bottom magnetic layers are also supplied with film electrodes (e.g., comprising tantalum (Ta), tantalum nitride (TiN), copper (Cu), and the like) to form an electrical connection for the memory cell to the lines of the MRAM.
Fabrication of a MRAM device comprises etch processes in which one or more layers comprising a MRAM film stack are removed, either partially or in total. The MRAM device comprises the layers that are generally formed from materials that may be easily oxidized, sensitive to corrosion or very thin, as well as may leave difficult to remove metal-containing post-etch residues upon the film stack. Such residues may build up along the sides of the film stack. The conductive residues or eroded layers may cause electrical short-circuits within a MRAM device, e.g., between the top and bottom magnetic layers, or may render the MRAM device to operate sub-optimally or not at all.
During etching a MRAM film stack, the conductive residues are repeatedly removed by cleaning the wafer in solvents comprising, in various combinations, hydrogen fluoride (HF), ammonium fluoride (NH4F), ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2), and the like. Such wet cleaning processes are disclosed, for example, in commonly assigned U.S. patent applications Ser. No. 10/218,244, filed Aug. 12, 2002 and Ser. No. 10/231,620 filed Aug. 29, 2002, which are incorporated herein by reference. Disadvantages of using the wet cleaning processes to remove residues and veils produced during fabrication of the MRAM devices include low productivity of the cleaning processes, lack of real time (i.e., in situ) end point detection, as well as a need in dedicated processing equipment.
Therefore, there is a need in the art for an improved method for removing conductive residue during fabrication of a MRAM device.